The present invention relates to an electronic timepiece (watch and clock) incorporating power generation means (generator) for generating electricity by utilizing external available energy, and particularly, to an electronic timepiece having a function of storing the electric energy generated by the power generation means, and driving time-indicating means for executing a time display operation by the agency of the electric energy stored.
There has lately become commercially practical an electronic timepiece provided with built-in power generation means for converting external energy such as optical energy, thermal energy, mechanical energy, and so forth into electric energy, and utilizing the electric energy as driving energy for executing a time display operation.
Among such electronic timepieces provided with the built-in power generation means, there are included a solar cell timepiece using a solar cell, a mechanical electric power generation timepiece converting mechanical energy generated by a rotary weight into electric energy and utilizing the same, and a thermoelectric power generation timepiece generating electricity by utilizing the difference in temperature between the opposite ends of each of thermocouples connected in series.
It is essential for these electronic timepieces provided with the built-in power generation means to have built-in means for storing generated electric energy therein while the external energy is available so that the timepieces are driven continuously and stably all the time even when the external energy is no longer available. Such an electronic timepiece has been disclosed in, for example, JP, 4-81754, B.
FIG. 7 shows an example of a conventional electronic timepiece provided with a built-in power generation means, including electric energy storage means.
With the timepiece, power generation means 10 is a solar cell, and the positive terminal thereof is grounded, forming a closed circuit with a first diode 43 and time-indicating means 21. The time-indicating means 21 is comprised of a time-indicating block 22 for executing time display by the agency of electric energy, and a capacitor 23 having capacitance of 22 xcexcF, which are connected in parallel.
Further, the power generation means 10 forms another closed circuit with a second diode 44, a first switching device 41, and storage means 30.
A second switching device 42 interconnects the negative terminal of the capacitor 23 and the negative terminal of the storage means 30 such that the capacitor 23 and the storage means 30 can be coupled in parallel.
A switch circuit 40 for performing transfer or interruption of electric energy among the power generation means 10, the storage means 30, and the time-indicating means 21 is comprised of the first switching device 41, the second switching device 42, the first diode 43, and the second diode 44.
Further, a first voltage comparator 16 compares a terminal voltage of the capacitor 23 with a first threshold value, and a second voltage comparator 17 compares the terminal voltage of the capacitor 23 with a second threshold value. The comparison result of the first voltage comparator 16 and that of the second voltage comparator 17 are caused to be inputted to a time-indicating block 22, thereby controlling the first switching device 41 by a first switching signal S21 outputted by a control circuit within the time-indicating block 22.
In this case, the first threshold value is xe2x88x922.0 V, and the second threshold value is xe2x88x921.5 V.
Further, a third voltage comparator 18 compares a terminal voltage of the storage means 30 with a third threshold value, and the comparison result thereof is caused to be inputted to the time-indicating block 22, thereby controlling the second switching device 42 by a second switching signal S22 outputted by the control circuit within the time-indicating block 22. In this case, the third threshold value is xe2x88x922.0 V as well.
The first, second, and third voltage comparators 16, 17, 18 perform a comparison operation intermittently in a cycle of one second, respectively.
In a circuit diagram shown in FIG. 7, upon the start of generation of electric energy by the power generation means 10, the capacitor 23 of small capacitance is first charged with the electric energy, and the time-indicating means 21 starts a time-indicating operation by the agency of the electric energy stored in the capacitor 23. At this point in time, the second switching device 42 is open.
Upon a voltage between the terminals of the capacitor 23 reaching 2.0 V or higher, and an input voltage to the first voltage comparator 16 becoming xe2x88x922.0 V or lower since the positive terminal thereof is grounded, the first voltage comparator 16 detects such a condition, and depending on the result of detection, the time-indicating block 22 closes the first switching device 41, thereby causing the storage means 30 to be charged.
Conversely, upon a voltage between the terminals of the capacitor 23 becoming lower than 1.5 V, and an input voltage to the second voltage comparator 17 becoming higher than xe2x88x921.5 V, the second voltage comparator 17 detects such a condition, and depending on the result of detection, the time-indicating block 22 opens the first switching device 41, thereby causing the capacitor 23 side of the time-indicating means 21 to be charged.
Further, upon a voltage between the terminals of the storage means 30 exceeding 2.0 V as the charging of the storage means 30 proceeds, and an input voltage to the third voltage comparator 18 becoming xe2x88x922.0 V or lower, the third voltage comparator 18 detects such a condition, and depending on the result of detection, the time-indicating block 22 closes the second switching device 42, thereby causing both the storage means 30 and the capacitor 23 to be charged.
However, the electric energy generated by the power generation means 10 undergoes variation depending on the external environment. For example, in the case of the solar cell, variation occurs mainly in quantity of electric current that can be outputted, and in the case of a thermoelectric power generation device, a generated voltage undergoes variation depending on the difference in temperature impressed from outside.
That is, depending on the external environment, the electric energy generated by the power generation means 10 undergoes an abrupt increase at times, thereby causing a voltage between the terminals of the capacitor 23 inside the time-indicating means 21 to undergo an abrupt rise.
As a result, there have occurred cases where an under-load driving operation of the time-indicating block 22 connected with the capacitor 23 in parallel becomes unstable, so that time display can not be executed properly.
It is possible to solve this problem by various means such as by increasing capacitance of the capacitor 23, by causing the respective voltage comparators to perform a comparison operation in a shorter cycle, and so forth, however, a large capacitance capacitor results in an increase of the size thereof, so that such a capacitor can not be incorporated in a small-sized electronic timepiece such as a wrist watch.
Further, since an amplifier such as the first, second, and third voltage comparators 16, 17, 18 has relatively large energy consumption, there has also arisen a problem that frequent activation of the voltage comparators deteriorates energy efficiency.
The invention has been developed to solve the above-described problems encountered by the conventional electronic timepiece provided with the built-in power generation means, and it is therefore an object of the invention to enable control of the under-load driving operation for time display and the charging of the storage means to be efficiently executed even if variation occurs to a terminal voltage of the power generation means or to that of the storage means.
To this end, an electronic timepiece according to the invention comprises: power generation means for generating electricity from external energy; storage means for storing the electric energy generated by the power generation means; time-indicating means for executing time display operation by use of the electric energy supplied from the power generation means or the storage means; a switching circuit comprising at least a plurality of switching devices, for executing transfer or interruption of the electric energy among the power generation means, the storage means, and the time-indicating means; voltage-measuring means for measuring a terminal voltage of the time-indicating means, being capable of deciding in which range the voltage is included among at least three levels of voltage ranges; and control means for controlling the switching circuit by determining a ratio of electric energy to be distributed between the storage means and the time-indicating means in a set period during charging of the storage means and the time-indicating means by the power generation means at any of at least three different ratios predetermined so that the ratios correspond to the voltage ranges one-to-one, according to results of measurement by the voltage measuring means.
The control means can be constituted so as to control the switching circuit by determining a ratio of supply time of charge current from the power generation means to the storage means to supply time of charge current from the power generation means to the time-indicating means in the set period during charging of the storage means and the time-indicating means by the power generation means at any of at least three different ratios predetermined so that the ratios correspond to the voltage ranges one-to-one, according to the voltage range decided by the voltage measuring means.
Or the control means may be constituted so as to control the switching circuit by determining a ratio of impedance of a charge current supply circuit from the power generation means to the storage means to impedance of a charge current supply circuit from the power generation means to the time-indicating means during charging of the storage means and the time-indicating means by the power generation means at any of at least three predetermined different ratios according to the voltage range decided by the voltage measuring means.
Further, the electronic timepiece according to the invention may comprise: power generation means for generating electricity from external energy; voltage-up means (booster means) for boosting a voltage generated by the power generation means; storage means for storing electric energy boosted by the voltage-up means; time-indicating means for executing time display operation by use of the electric energy supplied from the voltage-up means or the storage means; a switching circuit comprising at least a plurality of switching devices, for executing transfer or interruption of the electric energy among the voltage-up means, the storage means, and the time-indicating means; voltage-measuring means for measuring a terminal voltage of the time-indicating means, being capable of deciding in which range the voltage is included among at least three levels of voltage ranges; and control means for controlling the switching circuit by determining a ratio of electric energy to be distributed between the storage means and the time-indicating means in a set period during charging of the storage means and the time-indicating means by the power generation means via the voltage-up means at any of at least three different ratios predetermined so that the ratios correspond to the voltage ranges one-to-one, according to results of measurement by the voltage measuring means.
In such a case as described above, the control means can be constituted so as to control the switching circuit by determining a ratio of supply time of charge current from the voltage-up means to the storage means to supply time of charge current from the voltage-up means to the time-indicating means in the set period during charging of the storage means and the time-indicating means by the power generation means via the voltage-up means at any of at least three different ratios predetermined so that the ratios correspond to the voltage ranges one-to-one, according to the voltage range decided by the voltage measuring means.
Or the control means may be constituted so as to control the switching circuit by determining a ratio of impedance of a charge current supply circuit from the voltage-up means to the storage means to impedance of a charge current supply circuit from the voltage-up means to the time-indicating means during charging of the storage means and the time-indicating means by the power generation means at any of at least three predetermined different ratios according to the voltage range decided by the voltage measuring means.
Further, with either of the electronic timepieces as described above, the time-indicating means is preferably provided with electric energy amount control means for controlling an amount of electric energy consumed by the time-indicating means for executing time display so as to be within a predetermined range all the time according to the results of measurement by the voltage measuring means.
Furthermore, in the case of the time-indicating means comprising a stepping motor, the electric energy amount control means is preferably constituted so as to control an amount of electric energy consumed by the time-indicating means for executing time display so as to be within a predetermined range all the time by setting a pulse at which electric current is supplied to the stepping motor to any of a plurality of predetermined different shapes as selected according to the results of measurement by the voltage measuring means.
With any of the electronic timepieces as described above, the time-indicating means preferably comprises an auxiliary storage means for temporarily storing the electric energy.
With the electronic timepieces according to the invention constituted as described above, the electric energy generated by the power generation means can be distributed between the time-indicating means and the storage means at a suitable ratio of electric energy for charging the both. This enables efficiency of charging the storage means with the electric energy generated by the power generation means to be rendered better than before even if a cycle of the measurement is the same as before.
Further, even if an abrupt change occurs to the electric energy generated due to a change in the external environment, it is possible to prevent an abrupt change from occurring to a voltage between the terminals of the time-indicating means, so that time-indicating operation of the time-indicating means can be stabilized.